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Abstract
We present the data showing significant impact of scattering upon base-loss in the VIS/NIR region in bismuth (Bi), yttrium/lithium co-doped germano- and phospho-silicate optical fibers. The fibers were fabricated through standard modified chemical vapor deposition process in conjunction with solution-doping technique and their spectral loss (linear and nonlinear, at different excitation wavelengths) and emission properties were thoroughly studied. Among the features revealed for the fibers, the dependence of unbleached loss on wavelength obeyed (∼1/λ4) points on Raleigh scattering behind the phenomenon.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Since the first reports on lasing at ∼1.2 µm using Bi-doped fiber (BDF) [1,2], researches towards exploring such fibers and Bi-doped glasses for laser / amplifier applications were progressively developed [3–30]. Depending on BDF core-glass composition and fabricating conditions, Bi-related “active” centers (BACs) of different types, fluorescing in the NIR range (1.1-1.8 µm), can arise; see e.g. reviews [13–23]. Particularly, strong fluorescence in BDFs based on germano-silicate (GS) and phospho-silicate (PS) glasses, where specific BACs associated with Ge and P, was reported; in many cases, such fibers were shown to be good candidates for lasing / amplifying within 1.3-1.8 µm domain.
In spite of substantial success in the area, there remains misunderstanding in the physics of BDFs, which limits further progress in their practical usage. Among the challenging issues, the key one is the absence of a compromise view on BACs’ nature: opinions about types and structures of these centers are yet controversial. A separate problem is Bi concentration effects (viz. BACs clustering) in BDFs, one of consequences of which being rise of unbleached loss with increasing Bi content [5,25–30] that eventually stems from low solubility of Bi in silica due to its large atomic size. Particularly, the clustering phenomenon obstructs a high gain at increasing content of fluorescing BACs. As known, Bi ions always exist in multiple oxidation states in silicates. In this sense, another challenge inherent to Bi-doped glasses and BDFs is that it is technologically difficult, or even impossible, to stabilize Bi in a single oxidation state. Furthermore, if a BDF is pumped at a given wavelength, the excitation may be shared among BACs of different types, whereas its limited fraction only, inherent to BACs of single type, is converted to lasing, which may give rise to diminished laser efficiency.
Up till now, the most part of studies with BDFs concerned their applications for the NIR region; for instance, BDFs with GS or PS types of core-glass were demonstrated to lase at ∼1.3, ∼1.4, ∼1.5, and ∼1.6-1.8 µm. To mitigate the mentioned problem of low solubility of Bi in silica glass and, consequently, to meet the requirement of weakened BACs clustering, a line of research was performed with multicomponent glasses as hosts for Bi where such modifiers as Lithium (Li), Yttrium (Y), Hafnium, etc are used as co-dopants. According to the glass technology principles, with increasing content of a structural modifier such as Li or Y, interstitial gap in glass network can be increased via creating of a large amount of non-bridging oxygens (NBOs). This facilitates dissolving of such atoms with large atomic radii like Bi into silica glass and hence diminishes their clustering. This also leads to a higher probability of creating of low-valence Bi states such as Bi0, Bi+, and Bi2+ in glass network. Besides, co-doping with Y or Li facilitates the radiative transitions between electronic levels, which is expected to enhance emissive potential of Bi doped materials in VIS/NIR given that these oxidation states are the main structural components of BACs responsible for emissions in this spectral range. In GS or PS BDFs co-doped with Y or Li, it is easier achievable controllable generation of BACs of proper type in suitable amounts thanks to good solubility of Bi in such glasses [24].
The referred circumstances grounded our motivation to fabricate BDFs of Bi-Li-Ge, Bi-Y-Ge, and Bi-Y-P types and to examine their optical properties in the VIS/NIR region. We present here a spectral analysis of the fibers’ losses that reveals dominance of Raleigh scattering (RS) loss in overall BDFs’ attenuation within this spectral range. Given that the scattering issue is poorly addressed in the literature on BDFs, our results may throw more light on the matter.
2. Experimental
2.1 Fabrication and material properties
Bi-Y and Bi-Li co-doped GS/PS optical preforms were fabricated through standard modified chemical vapor deposition (MCVD) process in conjunction with solution-doping (SD) technique. The preforms obtained were subsequently over-jacketed by silica tubes using the rod-in-tube technique to manage cutoff wavelengths for ∼800 nm or less and finally drawn into fibers with ∼125-µm outer diameter, coated with polymer of a high refractive-index (RI). The basic parameters of the fibers are summarized in Table 1. Note that the elemental compositions of the BDF samples were measured applying electron probe micro-analysis (EPMA); cutoff wavelengths were obtained via standardized measurements of the fibers’ transmissions at straight and coiled placing; RI differences were measured using a fiber analyzer; numerical apertures (NA) were found in the step-index approximation. These data, along with the details of the BDFs’ fabrication, are provided in [24].
Table 1. BDFs’ parameters
2.2 Loss and emission spectra
Loss spectra of the BDFs were measured using the cutback method. White light from a fiber-adapted source (Yokogawa AQ4305) was launched into BDF samples through splices and the transmitted light was recorded by an optical spectrum analyzer (OSA) with optical band 400…1650 nm (ANDO 6315A). At the measurements, we dealt with BDF samples of varied lengths, avoiding bending of fiber samples. The measured transmission spectra were then re-calculated into the loss spectra, α0(λ); the results are shown in Fig. 1(a). Besides, in Fig. 1(b), are presented the white-light images of the BDFs’ core areas.
Fig. 1. (a) Loss spectra of BDFs: solid lines 1 (Bi-Li-Ge), 2 (Bi-Y-Ge), and 3 (Bi-Y-P). By arrows are shown the excitation wavelengths used in the experiments on measuring the emission spectra (Fig. 2) and nonlinear losses (Fig. 3). The dashed line is built using the data of modeling RS-loss in Bi-Y-Ge and Bi-Y-P fibers (refer to Fig. 4 and the text therein). (b) BDFs’ cross-sectional images: (top) Bi-Li-Ge, (middle) Bi-Y-Ge, and (bottom) Bi-Y-P.
As seen from Fig. 1(a), the characteristic spectral features of the fibers (viz. the presence of specific broad absorptions bands) correspond to the ones reported for Y/Li free BG/BP analogs. Worth noting, these bands, characteristic to Ge-Bi and P-Bi BACs, are superimposed with background loss that steadily grows towards shorter wavelengths, the well-known fact for BDFs of any kind; see e.g. [14–20]. This background loss so far had unclear provenance; however, as we show below (see Section 3), it is most likely produced by the RS process.
In Fig. 2, we demonstrate the BDFs’ emission spectra, obtained at different excitation wavelengths: 405, 520, 633, 720, and 905 nm; refer to Fig. 1a where these are marked by vertical arrows. When these are compared with analogous emission spectra known for Bi-doped Y/Li free Ge/P fibers, their similarity, even in details, is apparent.
Fig. 2. PL spectra of BDFs obtained at different excitation wavelengths: (a) 405 nm, (b) 520 nm, (c) 633 nm, (d) 720 nm, and (e) 905 nm. BDF lengths used are specified in insets. The asterisk in panel (c) highlights vanishing emission in Bi-Li-Ge fiber at 633-nm excitation.
Experimentally, fiber samples were in-core pumped through splices in the simplest forward geometry by commercial laser diodes (LDs) with single-mode output fibers (JDSU, Q-Photonics and Innolume). The LDs’ output fibers were almost lossless spliced with the BDFs. The spectra exemplified in Fig. 2 were collected using the same OSA; to meet equality of the circumstances, all these were obtained at each wavelength at the same launched power (∼4 mW). Such pump-level was chosen, on one hand, as sufficient to saturate BACs’ population inversion and, hence, output emissions while, on the other hand, as safe for registration with the OSA. Lengths (Lf) of fiber samples (specified in insets) were chosen to provide comparable optical densities (OD = α0Lf) of the BDFs, at either excitation wavelength. Thus, the emission spectra in Fig. 2 allow one to reveal the relative (vs. pump wavelength) fluorescence capacities of Bi-Li-Ge, Bi-Y-Ge, and Bi-Y-P fibers within the whole VIS/NIR range. Note that, for the fiber lengths chosen, the pump-light was sufficiently absorbed in the BDFs that ensured effective generation of BACs related emissions, only slightly re-absorbed in the fibers and so easily measurable by the OSA.
2.3 Nonlinear loss and scattering
An important for our further analysis (Section 3) issue is the behavior of nonlinear, viz. in function of pump power Pin, absorption (or loss) of the BDFs. The data revealing this behavior are presented in Fig. 3, for all excitation wavelengths used.
Fig. 3. Nonlinear loss αNL in function of launched pump power Pin in: (a) Bi-Li-Ge, (b) Bi-Y-Ge, and (c) Bi-Y-P fibers. The dependences αNL(Pin) are built in each case for all excitation wavelengths (of relevant colors). The small-signal losses (α0) at these wavelengths are obtained from Fig. 1; the dashed lines specify the residual losses at these wavelengths (αF).
In experiments, pump light from a LD was launched through a splice to a BDF sample of length Lf and its nonlinear transmission was measured (using a powermeter Thorlabs) as: TNL = Pout/Pin (Pout is unabsorbed pump power) that was then re-calculated into nonlinear absorption (loss) αNL via the relationship: αNL = –ln(TNL)/Lf. Such dependences were obtained for all BDFs and for different Lf in the broad range of pump powers Pin; the final results are presented in Fig. 3. Note that length of each BDF was chosen to be back-proportional to small-signal loss α0 (see the left parts of the panels in Fig. 3), ensuring nearly equal ODs at either excitation wavelength, likewise in the experiments on measuring the emission spectra (Fig. 2). The horizontal dashed lines in Fig. 3 mark the plateaus, to which residual losses αF(λ) approach at the high pump powers.
As seen from Fig. 3, the dependences αNL(Pin) strongly differ for different excitation wavelengths: for shorter ones, the loss-plateaus lie upper than those for longer ones. Also, there are notable differences in αF-values between the GS/PS BDFs co-doped with Y (panels (b) and (c)) and GS BDF co-doped with Li (panel (a)): in the latter, the αF-plateaus lie lower as the whole.
The residual (unbleached) loss in a BDFs may have diverse origins: these may arise in systems of BACs either via excited-state absorption [5,10,25–31] and up-conversion because of BACs clustering (in this case, a considerable part of excitation power is cycling within BACs’ clusters) [26,29], or thanks to such a phenomenon as scattering, or by “cumulative” effect of these contributions. Certainly, uncovering a dominant source of residual loss is a hard to solve task; however, as we show below, the issue may be properly addressed in our circumstances.
Figure 4 resumes, in double logarithmic plot, the trends that the residual losses αF vs. wavenumber of excitation (reciprocal of wavelength λ: 104/λ) obey for Bi-Y-P, Bi-Y-Ge, and Bi-Li-Ge fibers: refer to the dependences built by symbols of different colors. Accordingly, the solid lines of relevant colors (1, 2, and 3) fit the experimental data. As seen from Fig. 4, all these with a high accuracy obey the law ∼λ-4. The found law points on that RS stands behind growth of the residual (unbleached) loss with decreasing wavelength, αF(λ). [The explanations for the dotted and dashed lines in Fig. 4 are given in Section 3.]
Fig. 4. Dependences (symbols) of unbleached losses in BDFs upon excitation wavenumber for (1) Bi-Li-Ge, (2) Bi-Y-Ge, and (3) bi-Y-P fibers; solid lines are polynomic fits of the data. The dashed line (a) plots the RS-loss vs. reciprocal λ for un-doped silica. The dotted lines (b) and (c) plot the modeling results for Bi-Y doped GS / PS fibers, providing the fitting gate (at varying concentration of nanoparticles enriched with Bi and Y) for data 2 and 3. The arrows mark the excitation wavelengths.
Note that, for fibers Bi-Y-Ge and Bi-Y-P (where BACs responsible for resonant absorptions/emissions in VIS/NIR are of completely different kinds), the plotted dependences (2 and 3) are nearly undistinguishable; in the meantime, the dependence 1 (for Bi-Li-Ge fiber) is shifted downward, viz. to lower loss values. As we discuss in Section 3, this result suggests that the pattern of αF-rise with λ in the first case is governed by “heavier” scatters (most probably, by nanoparticles) of similar type and similar size and, also, of similar concentration, as compared to the second one, where “lighter” scatters of a different type of lesser size or of lesser concentration define the αF(λ) behavior.
Besides, as seen from Figs. 1(a) and 2 for Bi-Li-Ge, 633-nm and 720-nm excitations are outside the BACs resonant absorption bands of this fiber and the related emissions are weak or almost vanishing (see e.g. the asterisked spectrum in Fig. 2(c)). However, the experimental data in Fig. 4 for these two kinds of excitation fit well the dependence 1’ overall law. This may serve an additional justification that residual loss αF in this special case is entirely produced by scattering.
3. Discussion
3.1 BDFs’ overall state-of-the-art
First, briefly comment on the data reported in Figs. 1, 2 and 3. The shown loss and emission spectra of Bi-Li-Ge, Bi-Y-Ge, and Bi-Y-P fibers (Figs. 1a and 2) are in accordance to the ones, known for their Bi-doped GS and PS Y/Li free analogs. That is, the spectral positions, widths, and relative intensities of the resonant-absorption and emission bands in VIS/NIR in our BDFs are inherent to Bi-Ge, Bi-P, and Bi-Si BACs in silica glass. Note that the high Bi-contents accessed in our fibers (∼0.06-0.07 wt.%) (Table 1) resulted in the high level of BACs’ resonant-absorption peaks above the base-loss in VIS/NIR (Fig. 1a) and very intensive fluorescence of BACs in this spectral domain, yet at low pumps (Fig. 2). Furthermore, the data on bleaching of resonant absorption in different spectral bands of BACs (Fig. 3) reveal that bleaching powers are measured by ∼1 mW (in VIS) to ∼few mW (in NIR), which signifies that inversion in the systems of BACs is easily established yet at low-power LD excitation. Also, mention that almost no up-conversion emissions were observed in either BDF, which evidences negligible excited-state absorption within the spectral range of pump lights used; this fact correlates with the results [28] for Bi-doped GS/PS fibers. All this seems to be advantageous for laser/amplifier applications of the developed fibers.
3.2 Raleigh scattering on Bi-rich nanoparticles as a loss factor in BDFs
The experimental data obtained for unbleached loss αF, establishing dependences 1, 2, and 3 of Fig. 4 (refer to the symbols and fitting lines), point on that RS stands behind the rise of base-loss with decreasing wavelength since this behavior almost ideally obeys the law αF ∼ λ-4. On the other hand, for conventional un-doped silica fiber, the dependence of RS-loss vs. λ can be approximated by formula for pure silica: α$(\lambda )= {\alpha ^\ast }{\left( {\frac{{{\lambda^\ast }}}{\lambda }} \right)^4}$ , where α* = 1.7 dB/km at λ* = 0.85 µm; the result is shown in Fig. 4 by dashed line (a). Note that, for un-doped silica fiber, RS results from density fluctuations and compositional inhomogeneities of sizes much smaller than λ. As seen from Fig. 4, the experimental data plots for αF (λ) in the BDFs are drastically displaced from line (a) toward higher loss; the difference is ∼2.5…3 orders of magnitude. This may mean that scatters responsible for RS in the studied BDFs should be of a different kind, say, nanoparticles (NPs), produced in GS/PS core-glasses due to co-doping with Bi, Y, and Li.
The issue of creating of NPs or nanocrystalline inclusions in Bi-doped glass or fiber was touched in the past [32,33] and gets more attention nowadays, especially for BDFs [34–39], because the related problem of scattering may be a serious drawback given that BDFs are naturally lengthy active media where cumulative effect of scattering loss is strong. In [38,39], it was experimentally demonstrated that in BDFs with different chemical compositions, NPs and nano-crystallites varying in size from units to tens nm are frequently produced, even at low Bi contents. As known, creating of Bi-rich nanosized inclusions in Bi-doped materials is a culminating point of the “redox reaction” [40]
Let us attempt to estimate impact of RS on base-loss in VIS/NIR in the fabricated BDFs. First, note that we shall model the phenomenon for Y co-doped BDFs only, viz. for Ge-Y-Bi and P-Y-Bi fibers: refer to plots 2 and 3 in Fig. 4. It is known that co-doping with Y almost always stimulates creating of NPs in doped fibers: this not solely concerns Y-Bi co-doped silica fibers [41–43] but also rare-earth doped ones [44,45]. Emphasize here that our BDFs were fabricated applying the same technology as in [41–43]; thus, we consider that the result of TEM analysis revealing formation of Y,Bi-rich NPs [41–43] is applicable for our case, too. On the other hand, the case of Ge-Li-Bi fiber, see plot 1 in Fig. 4, cannot be addressed here properly because effect of co-doping with Li upon NPs’ formation, as far as we know, is yet unexplored. In the meantime, note that the fact of significantly lower RS-loss in Ge-Li-Bi fiber, as compared to Ge-Y-Bi / P-Y-Bi ones (Fig. 4), can be ascribed to the property of Li to assist in proceeding the redox reaction (1) (say, at preform collapsing) in the reverse direction due to increased O2 partial pressure and partial leakage out of Li2O. Accordingly, probability of formation of metallic Bi (Bi0) inclusions, their clustering, and NPs formation seem to be lower in Ge-Li-Bi fiber than in Ge-Y-Bi / P-Y-Bi fibers. In this sense, note that, as found in [37], co-doping with Li, on the contrary to that with Na or K, leads to diminished effect of Bi-colloids’ formation.
Modeling of dependences αF (λ) for fibers Ge-Y-Bi and P-Y-Bi was done using formula for RS on NPs (see e.g. [46]):
The results are plotted in Fig. 4 by lines (b) and (c). These two have been calculated for two NPs’ concentrations: N = 2×1017 cm-3 and N = 7×1017 cm-3, respectively, which are close to ∼0.1…0.3 fractions of overall Bi content (Table 1). These two lines in Fig. 4 establish the borders of fitting gate for the experimental dependences αF(λ) for Ge-Y-Bi and P-Y-Bi fibers. As seen, the presented modeling results fit well the experimental data.
Additionally, output of the modeling for N = 3.5×1017 cm-3, (at this N-value, nearly coincident data’ streams 2 and 3 in Fig. 4 are explicitly fit both) is presented by the dashed curve in Fig. 1(a). It is evident (merely compare in Fig. 1(a) the dashed curve with curves 2 and 3 for Ge-Y-Bi and P-Y-Bi fibers) the dominance of RS-loss on Bi-rich NPs in the attenuation spectra.
The role of RS in excessive loss in BDFs within the VIS/NIR range requires attention as clearly deteriorating: a search for measures to minimize it may be rigorous for further improvement of BDFs state-of-the-art. Especially, this concerns a task of making BDF-based lasers or amplifiers for the VIS spectral range, a nowadays actual issue [24]. As well, this would need a care in such circumstances when a BDF is pumped in VIS for being used as a laser medium beyond 1 µm: indeed, even in this case, notable scattering of pump-light along the fiber may become a serious problem. On the other hand, RS is certainly helpful, say, at making BDF-based random lasers; see e.g. [48].
4. Conclusions
We reported the data revealing an essential contribution of Raleigh scattering in base-loss in VIS-to-NIR for novel Bismuth-Yttrium and Bismuth-Lithium co-doped germano- and phospho-silicate optical fibers. The presented results seem to be useful for deeper understanding the physics of such and, probably, other Bismuth-doped silicate fibers.
Funding
Ministry of Education and Science of the Russian Federation (Minobrnauka) (K3-2018-23).
Acknowledgements
A.V. Kir’yanov acknowledges financial support via the Increase Competitiveness Program of NUST “MISIS” of the Ministry of Education and Science (Russian Federation) under Grant K3-2018-23. A. Halder, E. Sekiya, and K. Saito acknowledge the help and support of the Toyota Technological Institute staff; they are also thankful to the Director of the Toyota Technological Institute for supporting this work. All authors acknowledge Kohoku Kogyo Co., Ltd., Japan, for drawing the fibers.
References
1. E. M. Dianov, V. V. Dvoyrin, V. M. Mashinsky, A. A. Umnikov, M. V. Yashkov, and A. N. Gur’yanov, “CW bismuth fibre laser,” Quantum Electron. 35(12), 1083–1084 (2005). [CrossRef]
2. V. V. Dvoyrin, V. M. Mashinsky, E. M. Dianov, A. A. Umnikov, and A. N. Guryanov, “Absorption, fluorescence and optical amplification in MCVD bismuth-doped silica glass optical fibers,” in Proc. 31st European Conference on Optics Communications (Glasgow, Scotland, 2005) Paper Th.3.3.5, pp. 949−950.
3. I. Razdobreev, L. Bigot, V. Pureur, A. Favre, G. Bouwmans, and M. Douay, “Efficient all-fiber bismuth-doped laser,” Appl. Phys. Lett. 90(3), 031103 (2007). [CrossRef]
4. L. I. Bulatov, V. M. Mashinsky, V. V. Dvoyrin, E. F. Kustov, E. M. Dianov, and A. P. Sukhorukov, “Structure of absorption and luminescence bands in aluminosilicate optical fibers doped with bismuth,” Bull. Russ. Acad. Sci.: Phys. 72(12), 1655–1660 (2008). [CrossRef]
5. V. G. Truong, L. Bigot, A. Lerouge, M. Douay, and I. Razdobreev, “Study of thermal stability and luminescence quenching properties of bismuth-doped silicate glasses for fiber laser applications,” Appl. Phys. Lett. 92(4), 041908 (2008). [CrossRef]
6. S. Yoo, M. P. Kalita, J. Nilsson, and J. Sahu, “Excited state absorption measurement in the 900-1250 nm wavelength range for bismuth-doped silicate fibers,” Opt. Lett. 34(4), 530–532 (2009). [CrossRef]
7. M. A. Hughes, T. Suzuki, and Y. Ohishi, “Compositional optimization of bismuth-doped yttria–alumina–silica glass,” Opt. Mater. 32(2), 368–373 (2009). [CrossRef]
8. M. Peng, C. Zollfrank, and L. Wondraczek, “Origin of broad NIR photoluminescence in bismuthate glass and Bi-doped glasses at room temperature,” J. Phys.: Condens. Matter 21(28), 285106 (2009). [CrossRef]
9. Y. Fujimoto, “Local structure of the infrared bismuth luminescent center in Bismuth-doped silica glass,” J. Am. Ceram. Soc. 93(2), 581–589 (2010). [CrossRef]
10. A. V. Kir’yanov, V. V. Dvoyrin, V. M. Mashinsky, N. N. Il’ichev, N. S. Kozlova, and E. M. Dianov, “Influence of electron irradiation on optical properties of Bismuth doped silica fibers,” Opt. Express 19(7), 6599–6608 (2011). [CrossRef]
11. E. M. Dianov, S. V. Firstov, S. V. Alyshev, K. E. Riumkin, A. V. Shubin, V. F. Khopin, A. N. Gur’yanov, O. I. Medvedkov, and M. A. Melkumov, “A new bismuth-doped fibre laser, emitting in the range 1625–1775 nm,” Quantum Electron. 44(6), 503–504 (2014). [CrossRef]
12. A. V. Kir’yanov, S. H. Siddiki, Y. O. Barmenkov, S. Das, D. Dutta, A. Dhar, V. G. Plotnichenko, V. V. Koltashev, A. V. Khakhalin, E. M. Sholokhov, N. N. Il’ichev, S. I. Didenko, and M. C. Paul, “Hafnia-yttria-alumina-silicate optical fibers with diminished mid-IR (>2 µm) loss,” Opt. Mater. Express 7(7), 2511–2518 (2017). [CrossRef]
13. V. V. Dvoyrin, V. M. Mashinsky, and E. M. Dianov, “Efficient bismuth-doped fiber lasers,” IEEE J. Quantum Electron. 44(9), 834–840 (2008). [CrossRef]
14. V. V. Dvoyrin, V. M. Mashinsky, L. I. Bulatov, I. A. Bufetov, A. V. Shubin, M. A. Melkumov, E. F. Kustov, E. M. Dianov, A. A. Umnikov, V. F. Khopin, M. V. Yashkov, and A. N. Guryanov, “Bismuth-doped-glass optical fibers – a new active medium for lasers and amplifiers,” Opt. Lett. 31(20), 2966–2968 (2006). [CrossRef]
15. E. M. Dianov, A. V. Shubin, M. A. Melkumov, O. I. Medvedkov, and I. A. Bufetov, “High-power cw bismuth-fiber lasers,” J. Opt. Soc. Am. B 24(8), 1749–1755 (2007). [CrossRef]
16. I. A. Bufetov, S. V. Firstov, V. F. Khopin, O. I. Medvedkov, A. N. Guryanov, and E. M. Dianov, “Bi-doped fiber lasers and amplifiers for a spectral region of 1300-1470 nm,” Opt. Lett. 33(19), 2227–2229 (2008). [CrossRef]
17. I. A. Bufetov and E. M. Dianov, “Bi-doped fiber lasers,” Laser Phys. Lett. 6(7), 487–504 (2009). [CrossRef]
18. M. Peng, C. Dong, L. Wondraczek, L. Zhang, N. Zhang, and J. Qiu, “Discussion on the origin of NIR emission from Bi-doped materials,” J. Non-Cryst. Solids 357(11-13), 2241–2245 (2011). [CrossRef]
19. E. M. Dianov, “Bismuth-doped optical fibers: a challenging active medium for near-IR lasers and optical amplifiers,” Light: Sci. Appl. 1(5), e12 (2012). [CrossRef]
20. I. A. Bufetov, M. A. Melkumov, S. V. Firstov, K. E. Riumkin, A. V. Shubin, V. F. Khopin, A. N. Guryanov, and E. M. Dianov, “Bi-doped optical fibers and fiber lasers,” IEEE J. Sel. Top. Quantum Electron. 20(5), 111–125 (2014). [CrossRef]
21. H. T. Sun, J. Zhou, and J. Qiu, “Recent advances in bismuth activated photonic materials,” Prog. Mater. Sci. 64, 1–72 (2014). [CrossRef]
22. E. M. Dianov, “Nature of Bi-related near IR active centers in glasses: state of the art and first reliable results,” Laser Phys. Lett. 12(9), 095106 (2015). [CrossRef]
23. S. V. Firstov, S. V. Alyshev, K. E. Riumkin, A. M. Khegai, A. V. Kharakhordin, M. A. Melkumov, and E. M. Dianov, “Laser-active fibers doped with Bismuth for a wavelength region of 1.6–1.8 µm,” IEEE J. Sel. Top. Quantum Electron. 24, 1–15 (2018). [CrossRef]
24. A. Halder, A. V. Kir’yanov, E. H. Sekiya, and K. Saito, “Fabrication and study of basic optical properties of Bismuth-doped germano-silicate and phospho-silicate fibers for VIS/NIR applications,” Opt. Mater. Express 9(4), 1815–1825 (2019) [CrossRef] .
25. M. P. Kalita, S. Yoo, and J. Sahu, “Bismuth doped fiber laser and study of unsaturable loss and pump induced absorption in laser performance,” Opt. Express 16(25), 21032–21038 (2008). [CrossRef]
26. V. V. Dvoyrin, A. V. Kir’yanov, V. M. Mashinsky, O. I. Medvedkov, A. A. Umnikov, A. N. Guryanov, and E. M. Dianov, “Absorption, gain, and laser action in Bismuth-doped aluminosilicate optical fibers,” IEEE J. Quantum Electron. 46(2), 182–190 (2010). [CrossRef]
27. Q. Zhao, Y. Luo, Y. Tian, and G.-D. Peng, “Pump wavelength dependence and thermal effect of photobleaching of BAC-Al in bismuth/erbium codoped aluminosilicate fibers,” Opt. Lett. 43(19), 4739–4742 (2018). [CrossRef]
28. E. Ryumkin, M. A. Melkumov, I. A. Varfolomeev, A. V. Shubin, I. A. Bufetov, S. V. Firstov, V. F. Khopin, A. A. Umnikov, A. N. Guryanov, and E. M. Dianov, “Excited-state absorption in various bismuth-doped fibers,” Opt. Lett. 39(8), 2503–2506 (2014). [CrossRef]
29. A. V. Kir’yanov, V. V. Dvoyrin, V. M. Mashinsky, Y. O. Barmenkov, and E. M. Dianov, “Nonsaturable absorption in alumino-silicate bismuth-doped fibers,” J. Appl. Phys. 109(2), 023113 (2011). [CrossRef]
30. A. V. Kir’yanov, S. H. Siddiki, Y. O. Barmenkov, D. Dutta, A. Dhar, S. Das, and M. C. Paul, “Bismuth-doped hafnia-yttria-alumina-silica based fiber: spectral characterization in NIR to mid-IR,” Opt. Mater. Express 7(10), 3548–3560 (2017). [CrossRef]
31. S. Firstov, S. Alyshev, V. Khopin, M. Melkumov, A. Guryanov, and E. Dianov, “Photobleaching effect in bismuth-doped germanosilicate fibers,” Opt. Express 23(15), 19226–19233 (2015). [CrossRef]
32. L. Dimesso, G. Gnappi, A. Montenero, P. Fabeni, and G.P. Pazzi, “The crystallization behaviour of bismuth germanate glasses,” J. Mater. Sci. 26(15), 4215–4219 (1991). [CrossRef]
33. Y. T. Fei, S. J. Fan, R. Y. Sun, and J. Y. Xu, “Crystallizing behavior of Bi2O3-SiO2 system,” J. Mater. Sci. Lett. 19(10), 893–895 (2000). [CrossRef]
34. E. Haro-Poniatowski, M. Jimenez de Castro, J. M. Fernandez Navarro, J. F. Morhange, and C. Ricolleau, “Melting and solidification of Bi nanoparticles in a germanate glass,” Nanotechnology 18(31), 315703 (2007). [CrossRef]
35. G. Lin, D. Tan, F. Luo, D. Chen, Q. Zhao, and J. Qiu, “Linear and nonlinear optical properties of glasses doped with Bi nanoparticles,” J. Non-Cryst. Solids 357(11-13), 2312–2315 (2011). [CrossRef]
36. B. Xu, S. Zhou, M. Guan, D. Tan, Y. Teng, J. Zhou, Z. Ma, Z. Hong, and J. Qiu, “Unusual luminescence quenching and reviving behavior of Bi-doped germanate glasses,” Opt. Express 19(23), 23436–23443 (2011). [CrossRef]
37. R. Wan, Z. Song, Y. Li, Q. Liu, Y. Zhou, J. Qiu, Z. Yang, Z. Yin, Q. Wang, and D. Zhou, “Influence of alkali metal ions on thermal stability of Bi-activated NIR-emitting alkali-aluminosilicate glasses,” Chin. Opt. Lett. 12(11), 111601 (2014). [CrossRef]
38. A. S. Zlenko, V. M. Mashinsky, L. D. Iskhakova, S. L. Semjonov, V. V. Koltashev, N. M. Karatun, and E. M. Dianov, “Mechanisms of optical losses in Bi:SiO2 glass fibers,” Opt. Express 20(21), 23186–23200 (2012). [CrossRef]
39. L. D. Iskhakova, F. O. Milovich, V. M. Mashinsky, A. S. Zlenko, S. E. Borisovsky, and E. M. Dianov, “Identification of nanocrystalline inclusions in Bismuth-doped silica fibers and preforms,” Microsc. Microanal. 22(05), 987–996 (2016). [CrossRef]
40. S. Khonton, S. Morimoto, Y. Arai, and Y. Ohishi, “Redox equilibrium and NIR luminescence of Bi2O3-containing glasses,” Opt. Mater. 31(8), 1262–1268 (2009). [CrossRef]
41. A. V. Kir’yanov, A. Halder, Y. O. Barmenkov, S. Das, A. Dhar, S. K. Bhadra, V. V. Koltashev, V. G. Plotnichenko, and M. C. Paul, “Distribution of Bismuth and Bismuth-related centers in core area of Y-Al-SiO2:Bi fibers,” J. Lightwave Technol. 33(17), 3649–3659 (2015). [CrossRef]
42. S. Torrengo, M. C. Paul, A. Halder, S. Das, A. Dhar, J. K. Sahu, S. Jain, A. V. Kir’yanov, and F. d’Acapito, “EXAFS studies of the local structure of bismuth center in multicomponent silica glass based optical fiber performs,” J. Non-Cryst. Solids 410, 82–87 (2015). [CrossRef]
43. A. Halder, S. K. Bhadra, S. Bysakh, M. C. Paul, and S. Das, “Strong and broad visible emission of Bismuth doped nano-phase separated yttria-alumina-silica optical fibers,” Curr. Nanosci. 12(3), 309–315 (2016). [CrossRef]
44. A. Halder, M. C. Paul, S. W. Harun, S. K. Bhadra, S. Bysakh, S. Das, and M. Pal, “Visible and near infrared up-conversion luminescence in Yb3+/Tm3+ co-doped yttria-alumino-silicate glass based optical fibers,” J. Lumin. 143, 393–401 (2013). [CrossRef]
45. M. C. Paul, M. Pal, A. V. Kir’yanov, S. Das, S. K. Bhadra, Y. O. Barmenkov, A. A. Martinez-Gamez, and J. L. Lucio-Martinez, “Yb-doped yttria-alumino-silicate nano-particles based optical fibers: fabrication and characterization,” Opt. Laser Technol. 44(3), 617–620 (2012). [CrossRef]
46. H. C. Van De Hulst, Light Scattering by Small Particles (Dover, 1981).
47. M.C. Paul, S. Das, A. Dhar, D. Dutta, P.H. Reddy, M. Pal, and A.V. Kir’yanov, “Advanced nano-engineered glass-based optical fibers for photonics applications,” in Handbook of Optical Fibers (G.D. Peng, ed.), (Springer Nature Singapore Pte. Ltd., 2018).
48. I. A. Lobach, S. A. Kablukov, M. I. Skvortsov, E. V. Podivilov, M. A. Melkumov, S. A. Babin, and E. M. Dianov, “Narrowband random lasing in a Bismuth-doped active fiber,” Sci. Rep. 6(1), 30083 (2016). [CrossRef]
